3 research outputs found
Latéropulsion des saccades oculaires dans le syndrome de Wallenberg
IntroductionA lateropulsion of saccades is observed in Wallenberg syndrome. The similarity of this symptom with that observed after inactivation of the caudal fastigial nucleus in animals suggests a common pathophysiology.GoalsIs this disorder concerned with goal specification (as suggested by studies in the cat) or motor execution control of orientation (as in monkeys)? What functional role(s) should be attributed to fastigial efferents?MethodsBy a method based on electromagnetic induction, eye movements (microsaccades, saccades) and head movements directed toward a small static visual target are recorded in the monkey, before and afterpharmacological inactivation of the caudal fastigial nucleus (cFN). This inactivation is carried out by local injection muscimol (GabaâA agonist).ResultsIn the monkey, contrary to the cat, the dysmetria of saccadic gaze shifts after inactivation of NFc only results from a dysmetria of eye saccades. These oculomotor changes are associated with alterations in eye-head coupling and movement speed (Quinet & Goffart 2005, 2007). On the other hand, as in the cat, a fixation offset (of a much smaller magnitude) is observed when the monkey maintains its gaze directed towards a static target (Guerrasio et al. 2010).DiscussionAlterations in eye-head coupling and saccade velocity indicate a disorder in the execution of orienting movements in the non-human primate (Goffart et al. 2003, 2004). This deficit would result from a disturbance of the fastigo-reticular projections. The detailed study of microsaccades during visual fixation suggests a role of fastigioâcollicular projections in the oculomotor coding of the position of a foveal target.ConclusionThe study of eyeâhead coupling and visual fixation in Wallenberg syndrome should make it possible to say which model (cat or monkey) is the most appropriate for understanding its pathophysiology (Tilikete et al 2006).IntroductionUne latĂ©ropulsion des saccades est observĂ©e dans le syndrome de Wallenberg. La similitude de ce symptĂŽme avec celui observĂ© aprĂšs inactivation du Noyau Fastigial caudal chez lâanimal suggĂšre une pathophysiologie commune.ObjectifsCe dĂ©sordre concerne tâil la spĂ©cification du but (suggĂ©rĂ© par les Ă©tudes chez le chat) ou le contrĂŽle de lâexĂ©cution motrice de lâorientation (chez le singe)? Quel rĂŽle(s) fonctionnel(s) attribuer aux effĂ©rences fastigiales?MĂ©thodesPar une mĂ©thode basĂ©e sur lâinduction Ă©lectromagnĂ©tique, les mouvements oculaires (microsaccades, saccades)et cĂ©phaliques dirigĂ©s vers une petite cible visuelle statique sont enregistrĂ©s chez le singe, avant et aprĂšsinactivation pharmacologique du Noyau Fastigial caudal (NFc). Cette inactivation est rĂ©alisĂ©e par injection localede muscimol (agoniste GabaâA).RĂ©sultatsContrairement au chat, la dysmĂ©trie des mouvements dâorientation saccadique du regard aprĂšs inactivation du NFc rĂ©sulte, chez le singe, dâune dysmĂ©trie des saccades oculaires. Ces changements oculomoteurs sont associĂ©s Ă des altĂ©rations du couplage oeilâtĂȘte et de la vitesse des mouvements (Quinet & Goffart 2005, 2007). En revanche, comme chez le chat, un dĂ©calage de fixation (dâune ampleur beaucoup plus petite) est observĂ© lorsque le singe maintient son regard dirigĂ© vers une cible statique (Guerrasio et al. 2010).DiscussionLes altĂ©rations du couplage oeilâtĂȘte et de la vitesse des saccades indiquent un dĂ©sordre de lâexĂ©cution motrice de lâorientation chez le primate nonâhumain (Goffart et al. 2003, 2004). Ce dĂ©ficit rĂ©sulterait dâune perturbation des projections fastigioârĂ©ticulaires. LâĂ©tude dĂ©taillĂ©e des microsaccades pendant la fixation visuelle suggĂšre un rĂŽle des projections fastigioâcolliculaires dans le codage oculomoteur de la position dâune cible fovĂ©ale.ConclusionLâĂ©tude du couplage oeilâtĂȘte et de la fixation visuelle dans le syndrome de Wallenberg permettra de dire quel modĂšle (chat ou singe) est le plus appropriĂ© pour en comprendre la pathophysiologie (Tilikete et al 2006)